Hello Bill –
Yours is a wonderful site. I have learned so much just from reading here. Otherwise, I might have 100 more questions. One thing I have learned here is how important an accurate schematic is. I have seen a couple and so many wire colors and paths were wrong that you don’t know how much may be correct. So I wanted to know how much is the wiring schematic for a 1974 Mark IV.
But I was hoping you could get me out of a rut by telling me why the clips on my fuse box powered by the large black wire with green dots don’t have voltage. They are not switched (I don’t think) because there is no heavy black wire in the ignition switch. I pulled off all the tape in the factory harness back to the battery looking for a junction for it but it was not there either, only the heavy black wire with orange stripe which sprouted 4 yellow wires that fed two relays on the firewall and went into the connectors to the interior. The big black wire seemed to go to the blower motor resistor coil rack on the ATC system. Which makes no sense to me. I’m about to jump my fuse box to a heavy switched wire out of aggravation, but wanted to hear from you first.
I would appreciate your help,
Thank you ,
Hi John –
Wiring problems sure can be frustrating at times. No one can hazard a decent guess as to why you have no power at any connection at the fuse box without some meaningful diagnosis. The first test that I always make when following an electrical power path is to verify that my test light is working properly at the vehicles battery. Testing equipment can fail. Any testing such as you are describing should also be performed ( as you agree ) with the correct wiring diagram at your side. Circuit testing with the use of this diagram would also save you needing to unwrap the factory wiring harness.
A specific Wiring Diagram is needed so that you can diagnose the issues in proper sequence. We are able to supply you with most repair parts needed.